Windowed doors for self-cleaning ovens

ABSTRACT

Windowed doors for self-cleaning household ovens where the window assembly has a series of spaced parallel glass window panels secured in alignment with two of such panels near the oven cavity enclosing a dead-air insulating space, and a third of such glass window panels being separated from the oven cavity by two dead-air space enclosing glass panels, with the space between the third panel and the two dead-air enclosing panels being ventilated for replacement of heated air therein by natural circulation of cooler air, and a thin grid-like foraminous reflective coating on at least one of the glass panels disposed in the ventilated air space to reflect a relatively large proportion of radiant oven heat and to be cooled by the air wash during such ventilation.

[151 3,692,015 1 Sept. 19, 1972 United States Patent Chase et a1.

7/1965 Rosenau et al. [26/200 X 2/l968 Belliveau..................6/1969 .219/406 ....l26/2OO 126/200 X Huff..............

drisak, both of Northvme; Harold E. 3,457,138 Miller Mcxelvey Plymouthan of Mich Primary Examiner-Carroll B. Dority, Jr. [73] Assignee:Shatterproof Glass Corporation, y- C y, Greene & H ell Detroit, Mich.

June 1, 1971 ABSTRACT Windowed doors for selfcleaning household ovensbly has a series of spaced ls secured in alignment with the oven cavityenclosing a [22] Filed:

Appl. No.: 148,616

where the window assem parallel glass window pane Related U.S.Application Data [62] Division of Ser. No. 848,547

two of such panels near dead-air insulating space, and a third of suchglass window panels being separated from the oven cavit Aug. 8, 1969,Pat. No. 3,612,825.

by two dead-air space enclosing glass panels, with th space between thethird panel and the two dead-air enclosing panels being ventilated forreplacement of heated air therein by natural circulation of cooler air,g on at 606 5mm ,3 82 .4 B 2 mo 5 "2 0 m 0 o n "0 6 mm H "6 2 mwm mnr.mu 1 l W d S M UhF 1]] 2 8 555 iii and a thin grid-like foraminousreflective coatin [56] References Cited least one of the glass panelsdisposed in the ventilated air space to reflect a relatively largeproportion of UNITED STATES PATENTS radiant oven heat and to be cooledby the air wash during such ventilation.

5/1963 Grahn et al. ...........126/200 X 2/1965 3,168,089 Larkin...................126/200 X 5 Claims, 7 Drawing [Figures iiiiiiii Lliliitiill.

P'A'IENTEDSEP 19 m2 SHEET 1 [IF 4 FIG.

WV WILLIAM B. CHAS QT JOSEPH E. JENDRISAK a HAROLD E. McKELVEY BY M0304Queue 8 Jewel! ATTORNEYS PATENTEDSEP 19 m2 SHEET 2 BF 4 INVENTORS.WILLIAM B.CHASE, JOSEPH E JENDRISAKE HAROLD E. McKElLVEY BY Ma ay, Qzeeae a /owed ATTORNEYS PATENTED l 9 I972 3 6 92 015 sum 3 or 4ATTORNEYS WILLIAM B. CHASE. JOSEPH E. JENDRISAK a FIG- 6 HAROLD E.McKELVEY BY M0 604;, Gwene A? Jewell P'A'IENTEDSEP 19 I922 SHEET U 0F 4FIG? INVENTORS. CH ASE WILLIAM B.

JOSEPH E. JENDRISAK a HAROLD E. McKELVEY BY M0 (304;, gm 8 JewellATTORNEYS WINDOWED DOORS FOR SELF-CLEANING OVENS This application is adivision of application Ser. No. 848,547, filed Aug. 8, 1969, now US.Pat. No. 3,612,825.

THE INVENTION The present invention relates to windowed selfcleaningovens and more particularly to doors for such ovens having multiple-paneinsulating windows with air-cooled grid-like semi-transparent foraminousreflectors.

Self-cleaning ovens have been in use for many years (see, for example,Hurko U.S. Pat. No. 3,121,158). A typical household self-cleaning ovenhas a cooking range between 150 and 550F., and cleaning is accomplishedby raising the oven temperature to between about 150 and 950F.Housewives have insisted that their ovens be provided with windows topermit viewing of the food being cooked without opening the oven door,and oven manufacturers have provided such windows in the doors of theirself-cleaning ovens.

However, windows in self-cleaning ovens present very serious problemsbecause, during cleaning, relatively large amounts of heat escapethrough the window, greatly reducing the efficiency of the cleaningoperation and causing uneven heat distribution in the oven itself, andalso because the oven window becomes exceedingly hot, much hotter thanthe remainder of the oven exterior, thereby creating a safety hazard.

Oven manufacturers have, for many years, sought practical solutions tothese problems without success. Prior to the present invention, it wasthought that the safest and most practical approach to the problem was 0retains a relatively large amount of heat in the oven to provide amovable opaque metal shield which is placed across the window duringcleaning and to provide a safety mechanism which prevents activation ofthe cleaning cycle'until the movable shield is in place. The windowedself-cleaning ovens were made in this manner for many years prior tothis invention, but the equipment was relatively costly and inconvenientto use and has not been wholly effective in minimizing heat loss or inkeeping the outer window temperature within safe limits.

The present invention provides the long-sought solution to the aboveproblems and makes it possible, for the first time, to manufactureinexpensive self-cleaning ovens having safe, effective insulatingwindows without the expense, inconvenience and other disadvantagescharacteristic of previous constructions. Briefly, the present inventionsolves the problem by providing the oven door with a window whichincludes two spaced parallel glass panels disposed innermost with theirperipheral edges surrounded by a wrap-around member forming an enclosedchamber or dead-air space between the panels; at least one additionalwindow panel spaced outwardly from the two inner. panels; means forventilating the space between this additional panel and the innerpanels; and, a reflective, semitransparent, highly conductive metal griddisposed in said ventilated space, preferably on the outer surface ofthe outer panel of the aforesaid inner pair of panels.

The dead-air space between the inner panels serves as a partialinsulator. The decorative semi-transparent reflective metal grid permitsa view of the oven interior but reflects back into the oven cavity arelatively large cavity.

An object of the present invention is to provide an effective, low-costwindowed oven door for high temperature self-cleaning ovens.

A further object of the present invention is to provide a window forhigh temperature ovens which will minimize heat loss through the window.

A still further object of the present invention is to provide a windowfor self-cleaning ovens in which the temperature of the outer windowpanel will not exceed the manufacturers recommended safety level.

Another object of the present inventionis to provide a high temperatureself-cleaning oven with a windowed door in which no part of the outerwindow panel will exceed 230F. when the oven is in the heat cleaningcycle of about 750 to 950F. for 2 hours in F. ambient air. I

A further object of the present invention is to pro-. vide a windowassembly or windowed oven door for high temperature self-cleaning ovenswhich does not require inconvenient or expensive safety mechanisms suchas movable shields.

Further objects and advantages of the present invention will becomeapparent as the description proceeds.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims, the following description and the annexeddrawings setting forth in detail certain illustrative embodiments of theinvention, these being indicative, however, of but a few of the variousthings in which the principle of the invention may be employed.

In the annexed drawings:

FIG. 1 is a side elevational view, partly broken away and partly insection, of a household range embodying the present invention;

FIG. 2 is an enlarged fragmentary section elevational view of the doorof FIG. 1;

FIG. 3 is an enlarged fragmentary perspective sectional view of the doorof FIG. 1;

FIG. 4 is an enlarged fragmentary view of one corner of the door takenalong the lines 4-4 of FIG. 5 showing the reflective metal grid;

FIG. 5 is an enlarged elevational view, partly broken away and partly insection, taken along the line 55 of FIG. 6;

FIG. 6 is a perspective view of a second embodiment of the invention;and

FIG. 7 is a perspective view of a third embodiment of the presentinvention.

Referring more particularly to the drawings, in which like parts areidentified by the same numerals throughout the several views, there isshown in FIGS. 1 to 3 a household free-standing electric self-cleaningrange 1 having a top cooking surface 2 with a plurality of surfaceheating elements 3, an oven cavity 4 directly beneath the top cookingsurface 2 and formed by a box-like oven liner cooperating with afront-opening drop door 6. The oven cavity 4 is suppliedwith twostandard heating elements, namely, a lower baking element 7 and an upperbroiling element 8. Suitable thermal insulation 9, such as fiberglass orthe like, surrounds the oven liner 5 to retain the heat developed by theheating units 7 and 8 in the oven cavity 4 for a more efficientutilization of the heating energy as well as to retain the outer surfaceof the range body 10 at a relatively cool temperature which would not beinjurious to the human touch.

An oven lamp 11 is arranged in the rear wall 12 of the oven liner 5 toilluminate the oven cavity 4 in a conventional manner. Further, theopposite side walls of the oven liner carry the usual shelf-supportingmeans (not shown) which support one or more removable shelves in theoven cavity in the usual manner.

The range 1 is provided along the back edge of the top cooking surfacewith a raised backsplash 14 which contains the various circuit controlelements, switches, thermostats, clock timers, etc., which enable hehousewife to control the various heating elements of both the topcooking surface 2 and oven 4. Preferably, the heating elements and theirswitches are arranged to provide the normal cooking operations and thehigh temperature self-cleaning operations.

As best seen in FIG. 2, the windowed oven door 6 has a frame 15 which isgenerally of sheet metal construction and includes a front or outer doorpanel 16, a middle door panel 17, and a rear or inner door panel 18. Thefront door panel 16 has a narrow rearwardlyturned peripheral flange 19.The middle door panel 17 is of mating construction with the outer doorpanel 16 having a front-turned peripheral flange 20 which fits withinthe flange 19 of the front door panel 16.

The rear door panel 18 has a narrow front-turned peripheral flange 21and is mountedon the rear surface of the middle door panel 17. The innerdoor panel 18 has a diameter roughly corresponding to the inner diameterof the oven opening and, when the door 6 is in the closed position, theinner doorpanel 18 projects slightly into the oven cavity in the mannerof a plug, whereas the middle door panel 17 overlays the oven opening. Avapor and heat resistant gasket 22 is fastened to the middle door panel17 around the periphery of the inner door panel 18 to prevent escape ofheat and vapor around the door edges.

A handle 23 is mounted on the outer surface of the front door panel 16at the top portion of the oven door 6 and the door 6 is hinged at itsbottom edge to the range body.

A window assembly or unit 24 is located in the oven door 6 and isconstructed according to the present invention to maintain its outermostglass panel at a relatively low temperature when the oven is operatingin the high temperature cleaning range of about 750 to 950F. While thisis the preferred temperature range for cleaning operations, the upperlimit of this cleaning temperature range can be as high as about 1,050F.Above this temperature, however, the oven is likely to suffer enamelfailure and/or softening of the window glass.

The window assembly 25 includes three spaced substantially paralleltransparent glass panels 28, 29 and 30. Window apertures 25, 26 and 27are formed in the front, middle and rear door panels 16, 17 and 18,respectively, and are visually registering in the assembled door 6. Thethree transparent glass panels 28, 29 and 30 are secured in spacedparallel relation between the front and rear door panels 16 and 18 atthose window openings 25, 26 and 27. The glass panels 28, 29 and 30consist of a first or inner glass panel 28, a second or intermediateglass panel 29 adjacent to the first panel 28 and separated from theoven cavity 4 by the first panel 28, and a third or outer glass panel 30separated from the first panel 28 by the second panel 29, so that theglass panels 28, 29 and 30 are arranged in the order of first 28 tosecond 29 to third 30 proceeding from the oven cavity 4 out to the frontof the oven.

A first spacer member 31 is disposed between the first and second panels28 and 29 at their peripheral edges, and a second spacer member 32 islikewise disposed between the second and third panels 29 and 30 at theirperipheral edges. A wrap-around or clamping member 33 encloses theperipheral edges of all three glass panels 28 to 30 and cooperates withthe spacer members 31 and 32 to secure the panels 28 to 30 in spacedparallel relation. Vent apertures 34 are provided in the second spacermember 32. Additional vents 45 are also provided in the adjacent regionof the wrap-around member 33 so that the space between the second andthird panels 29 and 30 communicates with the space between the front andmiddle door panels 16 and 17. Additional vent apertures 35 are providedin the upper and lower edges of the door 6 so that heated air may escapefrom between the second and third glass panels 29 and 30, through theoven door 6, and into the ambient atmosphere outside the oven 1.

There are no vent apertures to ventilate the space between the first andsecond glass panels 28 and 29, so that such space is a dead-air spacetending to insulate the oven cavity 4 and retard heat loss at the window24. Additional dead-air spaces may be formed by employing additionalspaced parallel transparent panels, but a single dead-air space isusually satisfactory.

A thin semi-transparent metallic reflector 36 (the thickness of which isgreatly exaggerated in the drawings for purposes of illustration) in theform of a grid-like or foraminous reflective coating 36 is deposited onthe front or outer surface of the second glass panel 29, so that thereflector 36 is located in the ventilated or air-wash space between thesecond and third glass panels 29 and 30. This reflector is preferably ofgold or platinum or an alloy containing one or both of these since goldand platinum are highly conductive (having a thermal conductivity inexcess of 40 BTU/(ftFhLF/in.) at 212F. and can form thin opaque surfaceshaving low surface emissivity (less than about 0.50) between 750F. and950F., so that it reflects a vlarge amount of radiant heat and retainsvery little.

Platinum and gold are also relatively chemically inactive and resistoxidation and corrosion at oven cleaning temperatures. Thin layers ofthose materials retain satisfactory opacity at high temperatures. Thesecharacteristics make them highly suitable and preferred for use in thepresent invention. A platinumgold alloy may be used when a silver colorreflector is desired.

At high temperatures, the reflector 36 reflects a substantial proportionof the radiant heat emanating from the oven cavity 4, thereby reducingheat loss at the win dow 24. At the same time, heat that is picked up bythe foraminous reflector 36 is readily conducted away in the air wash sothat the space between the second and third members 29 and 30 is keptrelatively cool, thereby permitting the exposed portion of the outersurface of the outer or third glass panel 30 to be maintained at arelatively cool temperature, i.e., less than about 230F. when the oven 1is at a heat cleaning temperature of about 950F. for 2 hours in 70F.ambient air. Oven manufacturers specify that the room-side glass paneltemperature should not exceed 265F.

The foraminous reflector 36 has a plurality of apertures or foramens 37in regular disposition throughout, and the ratio of the reflectors totalreflective surface area, (i.e., the area of one side of the reflector 36less the sum of the areas of the foramens 37) to the total area of theviewing apertures 37 is preferably about 3 to 2 so that ones viewthrough the center of the glass panel 39 is about 60 percent obstructed.This ratio could be raised or lowered, without departing from the spiritof the present invention, although either visibility or heat retentionwould be reduced respectively. Accordingly, in order for the reflectorto both. transmit and reflect substantial portions of heat and lightemanating from the oven cavity, the ratio should not exceed about 3:1 orbe less than about 1:2. The

foramens 37 should be fairly small (preferably on the order of 3/64 inchsquare or about .02 square inch). As the foramen size in increased (withthe same ratio of reflective surface area to viewing area maintained atabout 3 to 2), so is the width of the opaque portions between theforamens 37, so visibility through the grid 36 becomes discontinuous andimpaired. In addition, distinguishable alternating hot and cool areasform on the outer (third) panel, and the hot areas tend to exceed safeand/or acceptable temperature levels. Accordingly, foramen 37 sizeshould not exceed about one-sixteenth sq. inch.

The reflector is preferably fired onto the glass in a thin coatingaccording to standard techniques well known in the art. One methodinvolves oil soluble compounds of gold and/or platinum and palladium,together with rhodium, silver and certain base metals in a resin/solventsystem. This compound is applied to the glass by silk-screen process andthen fired at a high temperature approaching the distortion point of theglass e.g., at 1,050F. or even higher where a very hard glass substrateis employed. For a grid-like or foraminous semi-transparent reflectorthe compound (commonly called liquid gold) is applied in sufficientquantities so that the residue of gold left after firing is sufficientlythick to be opaque and to retain opacity at oven cleaning temperaturesbut thin enough to cool readily in the air wash (e.g., on the order of1,500 Angstroms). t

The thin reflective metal coatings may be fired into the glass duringtempering of the glass, for example, when using such liquid gold. Veryattractive decorative grids may be formed on the glass in fine detailwhen using such coatings. The grid-like. foraminous coatings used in thepresent invention are not only pleasing to the eye but are also durableso as to be ideal for household ovens. Such foraminous coatings aresuperior to any other type of semi-transparent coating for use inself-cleaning ovens.

The term semi-transparent reflector" as used herein is understood toinclude, but not be limited to, a reflector of the type shown in thedrawings where visibly distinct foramens are formed in an otherwisesubstantially opaque reflective metal surface having a substantialthickness, such as 1,000 to 2,000 Angstroms. Such term also includesreflectors of the type where the metal coating is extremely thin (e.g.,less than 200 Angstroms) so that the metal itself appears to besemitransparent. This is without regard to whether the transparency isdue to minute discontinuities in the coating or whether the metal itselfis actually transparent due to its thinness, so long as the reflectorboth transmits and reflects substantial portions of heat and lightemanating from the oven cavity.

Accordingly, in alternative embodiments of the present invention, thereflector is a thin coating of gold or the, like, perhaps having athickness on the order of between about 50 and 200 Angstroms. This thincoating is applied to the glass in an even, substantially continuousfilm without visibly distinct foramens. It is nevertheless so thin as tobe semi-transparent and both transmits and reflects substantial portionsof heat and light emanating from the oven cavity.

Thin semi-transparent reflective coatings may be applied to the glass invarious ways, including by vacuum deposition, by electroplating, and. bythe sputtering process. Glass so treated is commercially available, soldunder the trademark Mirro-Pane". Suitable methods of applying thereflector metal to the glass are described in our copending allowedapplication Ser. No. 848,547. The entire disclosure of that applicationis incorporated herein by reference and made a part of thisspecification.

While gold, platinum or alloys of those metals are preferred forconstruction of the semi-transparent foraminous reflectors according tothe present invention, other metals or alloys such as nickel, chromium,copper, aluminum, silver and/or their alloys may be satisfactory incertain embodiments, although they are typically either less reflectiveand/or less resistant to corrosion.

Inasmuch as the two innermost glass panels reach relatively highvtemperature levels, those panels are preferably of heat resistantborosilicate glass (e.g., such as is sold under the registered UnitedStates Trademark Pyrex.) Such glass may be heated up to as high asl,200F. or higher without deformation or appreciable glowing, and itwithstands rapid temperature variations satisfactorily.

Returning to a description of FIGS. 1 to 3 inclusive, the window unit 24formed by the three glass panels 28 to 30, spacers 31 and 32, reflector36, and wraparound member 33, is mounted at the oven doors windowapertures 25 to 27 with L-shaped brackets 38 which are fastened to themiddle door panel 17. In order to guard against the escape of gases andvapors, the outer or third glass panel 30 of the window unit 24 isresiliently held against the inwardly turned flange 39 defining thewindow aperture 25 of the front panel 16, and the inner or first glasspanel 28 of the window unit is resiliently held against the outwardlyturned flange 40 defining the window aperture 27 of the rear door panel18. A heat resistant gasket (not shown) may be employed to seat thewindow unit 24 between the door panels 16 and 18 to seal againstescaping gases and vapors.

The oven 1 has an air circulation chamber 41 formed between the ovenframe 42 and the oven liner 5. An air intake vent 43 is provided in therear of the oven frame 42 at the lower rear of such chamber 41. Amechanical fan 44 is positioned in the chamber 41 at the vent 43 to drawcool air into the chamber 41. Vents (not shown) are provided in anysuitable portion of the oven frame 42 so that warm air in the chamber 41may escape and keep the side, front and rear walls of the oven frame 42relatively cool for safety.

A second embodiment of the present invention is shown in FIGS. 4 to 6,wherein FIG. 6 shows a gas selfcleaning range 50 of the type having aplurality of burners 51 below and an oven 52 above. The oven cavity 53has a side-hinged windowed door 54 covering its front opening. The range50 is of standard self-cleaning construction in many respects, having asheet metal outer frame 55 and an insulated inner oven liner 56 definingthe oven cavity 53. The heating control panel 57 is located to the rightof the windowed door 54.

The windowed oven door 54 has a frame 58 which is generally of sheetmetal fabrication and comprises a front or outer door panel 59, a middledoor panel 60,

and rear or inner door panel 61. The front door panel 59 has arearwardly extending flange portion 49 at its outer peripheral edgewhich overlays and mates with the inner and middle door panels 61 and60, which are integrally formed with one another, joined at theirperipheral edges by a common connecting portion 62. The front, middleand rear panels 59, 60 and 61 have rearwardly or frontwardly directedflange portions 63, 64 and 65, respectively, generally bordering thewindow opening. A glass window unit or assembly 69 is located in theoven door 54 and mounted on such flanges.

j The window assembly 69 includes three rectangular transparent glasspanels 70, 71 and 72 secured in spaced parallel relation between thefront and rear door panels 59 and 61 at the window opening. The firstglass panel 70 is adjacent to the oven cavity 53. The second orintermediate glass panel 71 is spaced forward of the first panel 70 andseparated from the oven cavity 53 by the first panel 70. A third glasspanel 72 is spaced forward of the second panel 71, being thus separatedfrom the first panel 70 by the second panel 71.

A first spacer member 73 of generally U-shaped cross section is disposedbetween the adjacent peripheral edges of the first and second glasspanels 70 and 71, and a second similarly shaped spacer member 74 islikewise disposed between the adjacent peripheral edges of the secondand third glass panels 71 and 72.

A wrap-around or clamping member 75 encloses the peripheral edges ofallthree glass panels 70 to 72 and cooperates with the spacer members 73and 74 to secure the glass panels 70 to 72 in spaced parallel relation.A plurality of ventilating apertures 77 are also provided in thatportion of the clamping member 75 adjacent the second spacer member 74so that the space between the second and third glass panels 71 and 72 isventilated to form an air-wash space in communication with the spacebetween the front and middle door panels 72 and 71. Additional ventapertures 78 and 79 are provided in the upper and lower edges of thedoor 54, i.e., in the rearwardly directed peripheral flange portion 49of the outer door panel 59, so that hot air between the second and thirdglass panels 71 and 72 may escape therefrom through the oven door 54,into the ambient atmosphere outside the oven 50.

There are no corresponding vent apertures to ventilate the space betweenthe first and second glass panels and 71, so that such space is adead-air space tending to insulate the oven cavity 53 and retard heatloss at the window 69.

A thin semi-reflective metallic reflector 80 in the form of a grid-likereflective metallic foraminous coating 80 with small foramens 89 isdisposed on the front or outer surface of the second glass panel 71 sothat it is located in the ventilated air-wash space between the secondand third panels 71 and 72. This grid 80 has the same general physicaland chemical characteristics as does the grid 36 described withreference to FIGS. 1 to 3, hereinabove. The thickness of the coating 80is greatly exaggerated for purposes of illustration and is on the orderof about 1,500 Angstroms in actuality. Such thickness is usually nogreater than 1,500 Angstroms and is preferably at least about 1,000Angstroms and no more than about 2,000 Angstroms.

Standard fibrous insulating material 81 fills the space between the rearand middle panels 71 and 72 outside the window area, i.e., between theclamping member 75 and the common portion 62 connecting the outer edgesof the rear and middle door panels 61 and 60.

A heat resistant gasket 82 encircles the window aperture of the reardoor panel 61, secured by a suitable bracket 83, to form an airtightseal at the interface of the oven door 54 and the oven body 55 toprevent the escape of heat and moisture vapor'from the oven cavity 53during operation.

A conventional door handle 84 is mounted on the front door panel 59.

The oven 50 has an air circulation chamber 85 formed between the ovenframe 55 and the oven cavity 53. The air circulation chamber 85 has anair outlet (not shown) in the upper region of the oven frame 55 topermit hot air to escape so that the side walls of the oven frame 55 arekept relatively cool during cleaning. A first fan (not shown) may beprovided at an air intake vent in the base of the oven frame (also notshown) to direct cool air into the air circulation chamber 85, but useof such a fan is optional. It is preferable to allow air to enter theintake vent naturally by convection.

A portion of the oven frame 55 at the lower front edge of the ovencavity 53 projects forward to extend beneath the lower peripheral edgeof the oven door 54 and thereby extend the air circulation chamber 85into that region. A plurality of apertures 86 are formed in thehorizontal surface 87 of that projecting portion of the oven frame 55 tocommunicate with the apertures 79 in the lower peripheral edge of theoven door 54 so that air may pass from the air circulation chamber 85into the air-wash space between the second and third glass panels 71 and72 housing the reflective metal foraminous coating 80. A fan 88 may bemounted in the air circulation chamber 85 on the inner surface of thefront wall of the oven frame 55 adjacent to and directed at theapertures 86 communicating with the apertures 79 in the lower peripheraledge of the oven door 54 so that relatively cool air from the aircirculation chamber 85 is forced into the air wash space to facilitatecooling of the oven door 54. While this fan 88 provides generally bettercooling, it is optional and can be eliminated to reduce cost and theoven door 54 will be cooled sufficiently by convection and the naturaldisplacement of hot air by cooler air.

A third embodiment of the present invention is shown in FIG. 7 wherein awindow assembly or unit 90 has four transparent glass panels 91 to 94,inclusive, secured inspaced parallel relation and adapted to be mountedin the door of a self-cleaning oven. The first glass panel 91 isintended to be mounted adjacent the oven cavity. A second orintermediate glass panel 92 is spaced forward of the first panel 91 sothat it would be separated from the oven cavity by the first glass panel91. A third or outermost glass panel 93 is separated from the firstpanel 91 by the second panel 92. And, in addition to those three panels91 to 93, a fourth panel 94 is disposed between the second and thirdpanels 92 and 93, so that the third panel 93 is spaced from the firstpanel 91 by the fourth panel 94 as well as by the second panel92.

First, second and third spacer members 95 to 97, inclusive, of U-shapedcross section are disposed between the adjacent peripheral edges of thefirst and second glass panels 91 and 92, the second and fourth panels 92and 94, and the fourth and third panels 94 and 93, respectively.

A wrap-around or clamping member 98 encloses the peripheral edges of allfour glass panels 91 to 94 and cooperates with the spacer members 95 to97 to secure the glass panels 91 to 94 in spaced parallel relation. Aplurality of ventilating apertures 99 are provided in both thehorizontal and vertical sides of the second and third spacer members 96and 97, and also in that portion of the clamping member 98 adjacent thesecond and third spacer members 96 and 97 so that the spaces betweenboth the second and fourth panels 92 and 94 and between the fourth andthird panels 94 and 93 are ventilated, to form airwash spaces, whereasthe space between the first and second panels 91 and 92 is completelyenclosed to form a dead-air space.

An oven door or wall for reception of the window unit 90 would beprovided with air circulation passages communicating between theaforesaid air-wash spaces and the ambient atmosphere.

A thin semi-transparent metallic reflector 100 in the form of agrid-like foraminous coating is disposed on the inner surface of thefourth glass panel 94 so that it is washed by air passing through thespace between the second and fourth panels 92 and 94. Alternatively, thereflector 100 may be disposed on the outside surface of the second panel92 or the outside surface of the fourth panel 94 or on the insidesurface of the third or outermost panel 93.

Reflective coatings of the type described may also be disposedsimultaneously on two separate glass panel surfaces in the windowassembly located in the air wash, such as on both sides of the fourthpanel 94. At least one of the two gridlike reflective coatings shouldhave a position which is fixed. The other coating may be movable withits associated glass panel but preferably has a fixed position with itsforamens aligned foraminous reflective coating, best :results areobtained using either one or two foraminous reflective coatings. It isalso possible to employ a gridlilte foraminous coating having foramensthatare not fully transparent but are semi-transparent. For example, theforamens may be partially or fully coated with a thin reflective metalcoating (for example, a gold coating with a thickness of 50 toAngstroms).

A window unit formed in the manner shown in FIG. 7 as described hereinprovides an admirable outer window surface temperature, e.g., less thanabout F. in a self-cleaning oven in the heat cleaning range of about950F. for 2 hours in 70F. ambient air. Accordingly, a window unit of thefour panel variety illustrated in FIG. 7 may be employed as a substitutefor the window units 24 and 69 shown in the self-cleaning ranges I and50 of FIGS. 1 to 3 and FIGS. 4 to 6.

The efficacy of a window assembly according to the present invention inproviding a relatively cool outer window surface is illustrated by thefollowing:

A standard gas-fueled self-cleaning oven range sold under the trademarkModern Maid by Tappan Corp. was specially fitted with a windowed ovendoor according to the present invention, replacing a solid door. Theparticular window assembly employed was similar to the third embodimentdescribed herein except that the outermost window panel (herein theso-called third" panel) was oversized (on the order of 15 inches X 22inches) to give the appearance of an all-glass oven door for decorativepurposes. The first and second glass panels (the inner lite and the liteadjacent thereto) were 0.140 inch X 5 31/32 inches X 5 31/32 inchesborosilicate and spaced 0.884 inch from one another. The so-calledfourth glass panel was 3/ 16 inch X 5 31/32 inches X 15 31/32 inchescrystal, spaced 0.523 inch outwardly from the second glass panel. Thesethree inner panels were held at their edges in fixed relation by a metalwrap-around or clamping member and a pair of metal spacer members ofsuitable dimensions and of the type described and illustrated herein.The entire assembly was mounted in the oven door approximately one-halfinch behind the large third or outer glass panel. A thin gold film wasdeposited on the inner surface of the fourth glass panel and theinter-panel space in which the gold film was located was ventilated by aplurality of 7/8 inch diameter circular vent apertures spaced aboutone-sixteenth inch along the outermost spacer member and also in theclamping member adjacent that spacer. The upper edge of the oven doorwas similarly vented. The oven door included a metal inner panelpositioned generally above the innermost or first glass panel. A secondmetal panel was mounted frontward of and parallel to the inner doorpanel and was positioned generally above the second glass window panel,the space between the aforesaid metal door panels being filled with astandard heat insulating material, such as asbestos. A third metal panelwas mounted frontward of and parallel to the second metal panel and waspositioned generally above the fourth glass panel. The space between theaforesaid second and third metal door panels was open to permitcirculation of air from the window space housing the gold film to thevents in the upper edge of the oven door. A similar passage was affordedin the lower region of the oven door for the intake of cool air. lnaddition, the space between the front (third) oversize glass panel andthe fourth glass panel was ventilated at the upper and lower oven dooredge so that there was an air wash on both sides of the fourth glasspanel bearing the gold film. The gold film was opaque, but provided withhorizontally and vertically aligned 3/64 inch square apertures regularlyspaced three sixty-fourths inch apart so that the gold coating formed asemi-transparent grid. The gold grid was bounded by a solid 1% inch goldperipheral border.

The oven was operated over its standard cleaning cycle, comprising a15-hour warm-up period and a subsequent 2-hour cleaning period. Astandard Leeds & Northrup potentiometer was used to obtaincontemporaneous measurements at regular intervals of the temperatures of(a) the air in the room containing the oven, (b) the outer or room-sidesurface of the third or outer glass panel taken at a point opposite theupper edge of the fourth glass panel, and (c) the oven interior takenadjacent the upper edge of the oven door. These temperature values areset forth in Table 1.

TABLE 1 Room Temp. Outside Glass Oven Time (F.) Temp. (F.) Temp.

Temperature variance in columns (1:) and (c) after 0:50 are due tothermostatic control; values represent range of temperatures occurringduring 3-5 minute time intervals following time indicated.

From the above table, it can be seen that the present invention providesan oven window for a self-cleaning oven which is safe, minimizes heatloss, and is well within the specifications of the oven manufacturers.

In various embodiments of the present invention, spacing of the glasspanels in three-panel units of the type illustrated in FIGS. l-6 hereinmay vary, but spacing on the order of 1 inch between adjacent glasspanels is generally preferred, providing satisfactory insulatingcoolingcharacteristics in a relatively compact unit. A four-panel unit of thetype illustrated in FIG. 7 preferably embodies approximately l-inchspacing between the first and second panels, but the spacing between thesecond and fourth panels and between the fourth panel and thirdoutermost panel is preferably on the order of one-half inch. Thus thetotal width of the spaces between panels in the four-panel unit ispreferably no more than 2 inches and the distance between the inner faceof panel 91 and the outer face of panel 93 may be less than 3 inches.

Except for the thickness of the gridlike foraminous reflective coatings,the drawings are drawn substantially to scale to facilitate anunderstanding of the invention, but it will be apparent that the sizeand shape of a household self-cleaning oven may vary somewhat from whatis illustrated herein.

It will be understood that, in accordance with the provisions of thepatent laws, variations and modifications of the specific apparatusshown herein may be made without departing from the spirit of theinvention.

Having described our invention, we claim:

1. A hinged oven door for closing a door opening in a household oven,said door comprising:

a hollow sheet metal frame having a central opening and a window closingsaid opening, the rear of said hollow frame which is adapted to close anoven cavity being covered with insulation surrounding and in abuttingrelationship with said window unit;

said window comprising four transparent panels mounted in predeterminedspaced parallel relation in said central opening including an innerglass panel, a first intermediate glass panel near and spaced from saidinner panel, a second intermediate glass panel outwardly of said firstintermediate panel and spaced therefrom, and an outer transparent panelspaced from said second panel, said first intermediate panel beinglocated between said inner panel and said second intermediate panel,said second panel being located between said first panel and said outerpanel;

means essentially sealing the space between said inner panel and saidfirst intermediate panel to provide an insulating dead-air space betweensaid panels and near the inner side of the oven door;

a gridlike foraminous reflective coating located on said secondintermediate panel, the foramens of said coating having an average areano greater than 0.02 square inch, said coating having a thickness nogreater than about 1,500 Angstroms and being formed of a substantiallynon-chemically-reactive metal having a thermal conductivity in excess ofabout 40 BTU/ (ftFhr. F/in.) at 212F. and a surface emissivity less thanabout 0.50 throughout a temperature range between 750 and 950F. andselected from the group consisting of gold, platinum and alloysthereoff;

a cool air inlet means in the lower part of said door communicating withthe spaces on both sides of the panel provided with said reflectivecoating, and a warm air outlet means in the upper part of said doorcommunicating with said air inlet means, so that, when heat escapesthrough said dead-air space, substantial amounts of the escaping heatimpinge upon said gridlike foraminous reflective coating, portions ofwhich are reflected back toward the inner panel and other portions ofwhich are absorbed by said coating, said coating being cooled by theflow of air across it from said air inlet means to said outlet means tomaintain the outermost exposed surface of the outer transparent panel ata temperature below 230F. when the door is exposed to an oventemperature of 950F.,said air inlet and air outlet means providing anatural upward circulation of air over the inner and outer faces of saidsecond panel, the ratio of the total reflective surface area of saidgridlike foraminous coating to the total area of the foramens of saidcoating being between 311 and 2. An oven door as defined in claim 1wherein said reflective coating has a thickness of at least 1,000Angstroms.

3. An oven door as defined in claim 1 wherein a second gridlikeforaminous reflector is provided between said first intermediate paneland said outer panel, said second reflector being mounted in apredetermined position during normal use to permit viewing through thedoor.

4. An oven door as defined in claim 3 wherein said second foraminousreflector is mounted in a fixed posi tion relative to the firstreflector.

5. An oven door as defined in claim 4 wherein said second reflectorcomprises a reflective coating on one face of said second intermediatepanel and said first reflective coating is located on the opposite faceof said second panel.

1. A hinged oven door for closing a door opening in a household oven, said door comprising: a hollow sheet metal frame having a central opening and a window closing said opening, the rear of said hollow frame which is adapted to close an oven cavity being covered with insulation surrounding and in abutting relationship with said window unit; said window comprising four transparent panels mounted in predetermined spaced parallel relation in said central opening including an inner glass panel, a first intermediate glass panel near and spaced from said inner panel, a second intermediate glass panel outwardly of said first intermediate panel and spaced therefrom, and an outer transparent panel spaced from said second panel, said first intermediate panel being located between said inner panel and said second intermediate panel, said second panel being located between said first panel and said outer panel; means essentially sealing the space between said inner panel and said first intermediate panel to provide an insulating dead-air space between said panels and near the inner side of the oven door; a gridlike foraminous reflective coating located on said second intermediate panel, the foramens of said coating having an average area no greater than 0.02 square inch, said coating having a thickness no greater than about 1,500 Angstroms and being formed of a substantially non-chemically-reactive metal having a thermal conductivity in excess of about 40 BTU/ (ft.2hr. *F/in.) at 212*F. and a surface emissivity less than about 0.50 throughout a temperature range between 750* and 950*F. and selected from the group consisting of gold, platinum and alloys thereoff; a cool air inlet means in the lower part of said door communicating with the spaces on both sides of the panel provided with said reflective coating, and a warm air outlet means in the upper part of said door communicating with said air inlet means, so that, when heat escapes through said deadair space, substantial amounts of the escaping heat impinge upon said gridlike foraminous reflective coating, portions of which are reflected back toward the inner panel and other portions of which are absorbed by said coating, said coating being cooled by the flow of air across it from said air inlet means to said outlet means to maintain the outermost exposed surface of the outer transparent panel at a temperature below 230*F. when the door is exposed to an oven temperature of 950*F., said air inlet and air outlet means providing a natural upward circulation of air over the inner and outer faces of said second panel, the ratio of the total reflective surface area of said gridlike foraminous coating to the total area of the foramens of said coating being between 3:1 and 3:2.
 2. An oven door as defined in claim 1 wherein said reflective coating has a thickness of at least 1,000 Angstroms.
 3. An oven door as defined in claim 1 wherein a second gridlike foraminous reflector is provided between said first intermediate panel and said outer panel, said second reflector being mounted in a predetermined position during normal use to permit viewing through the door.
 4. An oven door as defined in claim 3 wherein said second foraminous reflector is mounted in a fixed position relative to the first reflector.
 5. An oven door as defined in claim 4 wherein said second reflector comprises a reflective coating on one face of said second intermediate panel and said first refLective coating is located on the opposite face of said second panel. 